Buggy code:
public final class JavaConventions { private static final char fgDot = '.' ; private static final Scanner SCANNER = new Scanner ( ) ; private JavaConventions ( ) { } private static int indexOfEnclosingPath ( IPath checkedPath , IPath [ ] paths , int pathCount ) { } private static int indexOfMatchingPath ( IPath checkedPath , IPath [ ] paths , int pathCount ) { } private static int indexOfNestedPath ( IPath checkedPath , IPath [ ] paths , int pathCount ) { } public static boolean isOverlappingRoots ( IPath rootPath1 , IPath rootPath2 ) { } private static synchronized char [ ] scannedIdentifier ( String id ) { } public static IStatus validateCompilationUnitName ( String name ) { } public static IStatus validateClassFileName ( String name ) { } public static IStatus validateFieldName ( String name ) { } public static IStatus validateIdentifier ( String id ) { } public static IStatus validateImportDeclaration ( String name ) { } public static IStatus validateJavaTypeName ( String name ) { } public static IStatus validateMethodName ( String name ) { } public static IStatus validatePackageName ( String name ) { } public static IJavaModelStatus validateClasspath ( IJavaProject javaProject , IClasspathEntry [ ] rawClasspath , IPath projectOutputLocation ) { } public static IJavaModelStatus validateClasspathEntry ( IJavaProject javaProject , IClasspathEntry entry , boolean checkSourceAttachment ) { IWorkspaceRoot workspaceRoot = ResourcesPlugin . getWorkspace ( ) . getRoot ( ) ; IPath path = entry . getPath ( ) ; switch ( entry . getEntryKind ( ) ) { case IClasspathEntry . CPE_CONTAINER : if ( ( path != null ) && ( ( path . segmentCount ( ) ) >= 1 ) ) { try { IClasspathContainer container = JavaCore . getClasspathContainer ( path , javaProject ) ; if ( container == null ) { ClasspathContainerInitializer initializer = JavaCore . getClasspathContainerInitializer ( path . segment ( 0 ) ) ; String description = null ; if ( initializer != null ) <START_BUG> description = initializer . getDescription ( path ) ; <END_BUG> if ( description == null ) description = path . makeRelative ( ) . toString ( ) ; return new JavaModelStatus ( IJavaModelStatusConstants . INVALID_CLASSPATH , Util . bind ( "classpath.unboundContainerPath" , description ) ) ; } IClasspathEntry [ ] containerEntries = container . getClasspathEntries ( ) ; if ( containerEntries != null ) { for ( int i = 0 , length = containerEntries . length ; i < length ; i ++ ) { IClasspathEntry containerEntry = containerEntries [ i ] ; int kind = ( containerEntry == null ) ? 0 : containerEntry . getEntryKind ( ) ; if ( ( ( ( containerEntry == null ) || ( kind == ( IClasspathEntry . CPE_SOURCE ) ) ) || ( kind == ( IClasspathEntry . CPE_VARIABLE ) ) ) || ( kind == ( IClasspathEntry . CPE_CONTAINER ) ) ) { String description = container . getDescription ( ) ; if ( description == null ) description = path . makeRelative ( ) . toString ( ) ; return new JavaModelStatus ( IJavaModelStatusConstants . INVALID_CP_CONTAINER_ENTRY , Util . bind ( "classpath.invalidContainer" , description ) ) ; } IJavaModelStatus containerEntryStatus = JavaConventions . validateClasspathEntry ( javaProject , containerEntry , checkSourceAttachment ) ; if ( ! ( containerEntryStatus . isOK ( ) ) ) { return containerEntryStatus ; } } } } catch ( JavaModelException e ) { return new JavaModelStatus ( e ) ; } } else { return new JavaModelStatus ( IJavaModelStatusConstants . INVALID_CLASSPATH , Util . bind ( "classpath.illegalContainerPath" , path . makeRelative ( ) . toString ( ) ) ) ; } break ; case IClasspathEntry . CPE_VARIABLE : if ( ( path != null ) && ( ( path . segmentCount ( ) ) >= 1 ) ) { entry = JavaCore . getResolvedClasspathEntry ( entry ) ; if ( entry == null ) { return new JavaModelStatus ( IJavaModelStatusConstants . INVALID_CLASSPATH , Util . bind ( "classpath.unboundVariablePath" , path . makeRelative ( ) . toString ( ) ) ) ; } return JavaConventions . validateClasspathEntry ( javaProject , entry , checkSourceAttachment ) ; } else { return new JavaModelStatus ( IJavaModelStatusConstants . INVALID_CLASSPATH , Util . bind ( "classpath.illegalVariablePath" , path . makeRelative ( ) . toString ( ) ) ) ; } case IClasspathEntry . CPE_LIBRARY : if ( ( ( path != null ) && ( path . isAbsolute ( ) ) ) && ( ! ( path . isEmpty ( ) ) ) ) { IPath sourceAttachment = entry . getSourceAttachmentPath ( ) ; Object target = JavaModel . getTarget ( workspaceRoot , path , true ) ; if ( target instanceof IResource ) { IResource resolvedResource = ( ( IResource ) ( target ) ) ; switch ( resolvedResource . getType ( ) ) { case IResource . FILE : if ( Util . isArchiveFileName ( resolvedResource . getFileExtension ( ) ) ) { if ( ( ( checkSourceAttachment && ( sourceAttachment != null ) ) && ( ! ( sourceAttachment . isEmpty ( ) ) ) ) && ( ( JavaModel . getTarget ( workspaceRoot , sourceAttachment , true ) ) == null ) ) { return new JavaModelStatus ( IJavaModelStatusConstants . INVALID_CLASSPATH , Util . bind ( "classpath.unboundSourceAttachment" , sourceAttachment . makeRelative ( ) . toString ( ) , path . makeRelative ( ) . toString ( ) ) ) ; } } break ; case IResource . FOLDER : if ( ( ( checkSourceAttachment && ( sourceAttachment != null ) ) && ( ! ( sourceAttachment . isEmpty ( ) ) ) ) && ( ( JavaModel . getTarget ( workspaceRoot , sourceAttachment , true ) ) == null ) ) { return new JavaModelStatus ( IJavaModelStatusConstants . INVALID_CLASSPATH , Util . bind ( "classpath.unboundSourceAttachment" , sourceAttachment . makeRelative ( ) . toString ( ) , path . makeRelative ( ) . toString ( ) ) ) ; } } }

Fix:
description = initializer . getDescription ( path , javaProject ) ;